Hydraulic fracturing is generally applied after a borehole is drilled and a cased wellbore formed. Hydraulic fracturing employs fluid and material to create or restore fractures in a geological formation in order to stimulate production from new and existing oil and gas wells. The fracturing typically creates paths that increase the rate at which production fluids can be produced from the reservoir formations. In some instances, water and sand make up 98 to 99.5 percent of the fluid used in hydraulic fracturing. In addition, chemical additives may be incorporated in the water. The formulation varies depending on the well. Moreover, operating wells may be subjected to hydraulic fracturing to remain operating. Fracturing may allow for extended production in older oil and natural gas fields. Hydraulic fracturing may also allow for the recovery of oil and natural gas from formations that geologists once believed were impossible to produce, such as tight shale formations.
Hydraulic fracturing in development of an oil-and-gas well may involve injecting water, sand, and chemicals under high pressure through a wellbore into a geological formation in the Earth's crust. This process may create new fractures in the rock as well as increase the size, extent, and connectivity of existing fractures and bedding planes. Thus, hydraulic fracturing (also called fracing or fracking) is a well-stimulation technique in which rock is fractured by a pressurized liquid. The process can involve the high-pressure injection of fracing fluid (also labeled fracking fluid, frac fluid, etc.) into a wellbore to generate cracks in the deep-rock formations through which natural gas, petroleum, and brine will flow more freely. An example of fracing fluid is primarily water containing sand or other proppants. In some instances, the sand or other proppants may be suspended in the water with the aid of viscosity increasing agents. Other chemical additives may be added to the fracing fluid to reduce friction, such as in slick water. Fracing jobs may direct completion hardware, sand weights, and water volumes to place sand.
In sum, hydraulic fracturing is used in the oil and gas industry to increase the flow of oil and/or gas from a well. The producing formation is fractured open using hydraulic pressure and then proppants (propping agents) may be pumped into the oil well with fracturing fluid to hold the fractures or fissures open so that energy (pressure) can be applied (e.g., pumped fracing fluid) into the formation and converted to stress, to enhance the breaking of the rock. The result is the natural gas or crude oil can flow more easily up the well. Hydraulic fracturing is employed in low-permeability rocks such as tight sandstone, shale, and some coal beds to increase crude oil or gas flow to a well from petroleum-bearing rock formations. Hydraulic fracturing can be applied for vertical or deviated (e.g., horizontal) wellbores. A beneficial application may be horizontal wellbores in low-permeability geological formations having hydrocarbons such as natural gas, crude oil, etc. Massive hydraulic fracturing or high-volume hydraulic fracturing may be applied to gas or oil-saturated formations with low permeability (e.g., less than 0.1 millidarcy).